Waterborne paints, inks, and other coatings are used for a multitude of applications including interior and exterior coatings for paper, wood, architectural surfaces, and many more. These coatings are composed of a number of components such as latex, alkyd, or other binders, pigments or other colorants, water, coalescing agents, thickeners, solvents, and a number of surfactants for various purposes. With strict environmental legislation requiring the reduction of the amount of Volatile Organic Compounds (VOC) in coatings, it is desirable to have paint formulations with little or no VOC content. Common VOC components in paint include coalescing agents and glycol freeze-thaw stability additives, among others. Removing these has resulted in a number of formulation and composition challenges. However, due to competitive pressures, low VOC coatings and paints must maintain or exceed coating performance standards expected in the industry.
Since waterborne coatings are subject to freezing at low temperatures commonly experienced in shipping or storage in northern latitudes, there is significant interest in improving the freeze/thaw stability of latex paints. As a consequence of reducing or eliminating VOCs in latex paints due to government regulations, simple glycols such as propylene glycol (PG), commonly used to help improve freeze/thaw stability, are being eliminated. Many coalescing solvents such as Texanol (IBT) that are VOCs are also being eliminated requiring softer (lower Tg) latexes to be used instead of the traditional harder (high Tg) latexes. Softer latexes have poorer freeze/thaw stability characteristics than higher Tg latexes further increasing the need for non-VOC freeze/thaw stability additives.
For low VOC paint binder latexes, the average Tg is close to or below 0° C. so that little or no coalescent is needed to make a good coating after drying. However, latex binders with low Tg often cause grit when subjected to freeze/thaw cycles as well as exposure to mechanical shear. The resulting coating films are softer and tackier, even after fully dried, and are susceptible to blocking and dirt pick-up effects. Also, such low Tg latex binders and resulting latex paints are not stable, and gel in a cold environmental storage or transportation process. Freeze-thaw stability of low Tg latex binders and low VOC paints is critically important for transportation, storage, and practical applications. Thus, there is a need to develop latex paints and latex particle dispersions that meet zero or low VOC requirements and at the same provide excellent mechanical and film performance without sacrificing the freeze-thaw stability of those paints. This requires non-VOC freeze/thaw stability additives.
In traditional latex binders for architectural coatings, the glass transition temperature is between about 10° C. to about 40° C. These higher Tg latexes do not suffer from the grit, blocking, and other problems that the low Tg latexes do. However, architectural coating formulations based on them usually need coalescent agents and anti-freeze agents, both of which are typically high-VOC solvents. Thus, there is a need for non-VOC freeze/thaw stability additives for use with higher Tg latex binders.
Latex freeze-thaw (sometimes herein referred to as “F/T”) stability, including the freezing-thawing process, destabilization mechanism, and polymer structures, have been extensively studied since 1950. Blackley, D. C., Polymer Lattices-Science and Technology, 2nd Ed., Vol. 1, Chapman & Hall, 1997, gives a comprehensive review of colloidal destabilization of latexes by freezing. The freezing process starts with the decrease of temperature, which leads to the formation of ice crystals. The ice crystal structures progressively increase the latex particle concentration in the unfrozen water. Eventually latex particles are forced into contact with each other as the pressure of growing ice crystal structures, resulting in particle aggregation or interparticle coalescence.
To make a stable latex dispersion in aqueous medium or latex paints with freeze-thaw stability, various approaches have been employed. The addition of antifreeze agents, e.g. glycol derivatives, has been applied to latex paint to achieve freeze-thaw stability. Thus, latex paints include anti-freeze agents to allow the paints to be used even after they have been subjected to freezing conditions. Exemplary anti-freeze agents include ethylene glycol, diethylene glycol, and propylene glycol. For a more detailed discussion see Bosen, S. F., Bowles, W. A., Ford, E. A., and Person, B. D., “Antifreezes,” Ullmann's Encyclopedia of Industrial Chemistry, 5th Ed., Vol. A3, VCH Verlag, pages 23-32, 1985. However, since these simple glycols are VOCs, a low or no VOC requirement for the formulated paint means that the glycol level has to be reduced or eliminated.
A number of methods to achieve freeze/thaw stability are known in the art. Farwaha et. al. (U.S. Pat. No. 5,399,617) discloses the use of copolymerizable amphoteric surfactants and discloses latex copolymers comprising the copolymerizable amphoteric surfactants to impart freeze-thaw stability to the latex paints. Zhao et. al. (U.S. Pat. No. 6,933,415 B2) discloses latex polymers including polymerizable alkoxylated surfactants and discloses the low VOC aqueous coatings based on them have excellent freeze-thaw stability. Farwaha et. al. (U.S. Pat. No. 5,610,225) discloses incorporating a monomer with long polyethylene glycol structures to achieve stable freeze-thaw latex. Okubo et. al. (U.S. Pat. No. 6,410,655 B2) discloses freeze-thaw stability of latex polymers including ethylenic unsaturated monomers.
It is well known that certain nonionic surfactants impart varying degrees of freeze/thaw stability to latexes; however, the levels required to impart freeze/thaw stability vary as a function of the Tg of the polymers and the propylene glycol level. Some of these nonionic surfactants are disclosed in U.S. Pat. No. 7,906,577 and in U.S. Pat. No. 8,304,479. Some of these can also function as open time extenders.
Another one of the challenges of formulating waterborne coatings is achieving an acceptable balance of properties both during the film application and drying process as well as in the final film. There is a competition between the requirements for adequate workability time of the coating with appropriate film formation and recoat behavior. The period in which irregularities in a freshly applied coating can be repaired without resulting in brush marks is referred to as the open time, while the period in which a coating can be applied over an existing paint film without leaving lap marks is deemed the wet edge time.
Aqueous coatings generally employ dispersed high molecular weight polymers as binders. These binders often provide short open times when the coating is dried since the dispersed polymer particles tend to be immobilized quickly in the edge region of an applied coating. As a result, the viscosity of the coating increases rapidly, which leads to a limited window of workability. Small molecule alkylene glycols such as ethylene and propylene glycol are routinely incorporated in aqueous coatings as humectants, but are considered to be VOCs. Thus, there is also a need for low VOC additives to improve open time and wet edge in aqueous coatings.
As mentioned above, surfactants are common components of waterborne coating formulations. They have many functions including dispersing pigments, wetting the substrate, improving flow and leveling, etc. However, once the coating has been applied to a substrate the surfactant is no longer needed. In fact, the presence of the surfactant often degrades the moisture sensitivity of the coating. Other coating properties can be negatively affected as well. This is largely due to the mobility of the surfactant polymers. For example, locally high concentrations of surfactant molecules can form in the coating from the coalescence of surfactant-coated micelle spheres. When the coating is exposed to water, these unbound surfactant molecules can be extracted from the coating leaving thin spots or pathways to the substrate surface. This can result in “blushing” and corrosion of the substrate.
Since surfactants have a number of deleterious effects on the finished coating and add cost to the coating formulation, minimizing their use would be desirable. A non-VOC additive that had multiple functions in the formulation such as imparting freeze/thaw stability, and extending open time and wet edge, and improving coalescence, could reduce the cost of and improve the performance of the finished coating.
The present invention provides alkoxylated styrenated phenols and naphthols that have been derivatized with allyl glycidyl ether as additives to impart WE/OT to Semigloss paints. Note that the study was done with acrylic latexes. Different results may be obtained with Vinyl Acrylic or Vinyl Acetate Ethylene (VAE) latexes since they are more hydrophilic. The “Martha Stewart Paint was a vinyl acrylic according to the label. Glidden has manufactured the paint under the Martha Stewart label until last year. Now, they still manufacture that paint but under the Glidden Interior Premium Paint (Semigloss) label. The Martha Stewart colors still work with the paint since it identical to the paint made in the past.